The present invention relates to a mechanical seal of the type which includes a rotatable member and a non-rotatable member provided with confronting radial faces and which are biased into rubbing engagement, and more particularly to a seal of this type which includes a laminated holder and a low-friction insert which forms one of the seal members.
Mechanical face seals of the type of which the present invention relates are used to seal an opening in the wall of a pressurized container through which a rotatable shaft extends. These seal assemblies include rings one of which is non-rotatably carried by the container and the other fixed to the shaft. One of the rings is provided with an insert constructed of a low friction material having a radial face which confronts a machined radial face on the other ring. One of the rings is biased toward the other so that the confronting faces of the rings rubbingly engage and maintain a pressure seal between the shaft and container wall.
The low friction insert is a non-metallic annular member press fitted in a holder, usually a metallic ring. It is important that the holder and insert assembly remain stable i.e., not distort or become loose during operation of the device. To this end, it is important that this assembly remain stable and resist distortion and separation throughout a range of temperatures which are expected to develop on the seal during its use, and under stresses which arise as a result of pressure in the container and centrifugal forces during rotation of the seal.
It will be appreciated that temperature rise occurs mainly from the sealed fluid in the container and from friction during use of the seal and causes the assembled holder and insert to expand. The coefficient of expansion of the metallic holder is different from that of the non-metallic insert so that a sufficient temperature rise can cause the insert to become loose in the holder thereby destroying the seal. Also, sufficient expansion of the holder relative to the insert can weaken the connection between their parts allowing distortion of the assembly and resultant seal loss.